Method for regulating the maximum speed of a working machine and associated hydrodynamic coupling

ABSTRACT

The invention relates to a method for regulating the maximum speed of a working machine ( 12 ), in particular an air compressor in a vehicle. Said working machine is driven by means of a motor ( 10 ), using a hydrodynamic coupling ( 11 ), which comprises a working chamber ( 3 ) that is partially or fully filled with a working medium for transmitting a torque from a drive side ( 11.1 ) equipped with an impeller ( 1 ) to a driven side ( 11.2 ) equipped with a turbine wheel ( 2 ). The method comprises the following steps: the speed of the working machine, of the driven side of the hydrodynamic coupling, of the drive side of the hydrodynamic coupling and/or of the motor is detected; a maximum permissible value for the speed is defined and compared to the detected speed; if the detected speed exceeds the maximum permissible value, the quantity of working medium in the working chamber of the hydrodynamic coupling is automatically reduced by the opening or passage of medium through an outlet that is connected to the working chamber.

The invention concerns a process to regulate the maximum rotation speed of a working machine, where the working machine is powered by a motor via a hydrodynamic coupling. The invention concerns specifically a process to regulate the maximum rotation speed of an air compressor in a vehicle, where the compressor is powered by the motor of the vehicle, specifically an internal combustion engine, via a hydrodynamic coupling and is embodied, for example, as a reciprocating piston air compressor to supply the compressed air system of the vehicle.

The adjustment of the rotation speed of a working machine by the adjustment of the fill level of a hydrodynamic coupling incorporated between the working machine and the motor powering the working machine is known; for example, see the publication WO 98/32987. There the adjustment of the fill level is essentially accomplished by interrupting the addition of working medium after the maximum fill level of the working space has been reached.

The known adjustment of the fill level is complicated in terms of the apparatus required and requires various adjustment components, such as pressure sensors, valves and/or scoop tubes. Particularly in an application of a hydrodynamic coupling in a vehicle, advantageously in the drive train between air compressor and the motor of the vehicle, in order to be able to turn the air compressor on and off and simultaneously dampen the vibrations and avoid a transmission of torque from the air compressor to the vehicle motor or the transmission of the vehicle motor, the known design of fill-adjusted hydrodynamic couplings is too complicated and not optimally suited to the rotation speed control of the working machine, specifically the air compressor.

A further option to limit the maximum rotation speed of a vehicle air compressor would be to use the motor control to limit or lower the motor rotation speed. However, given that the vehicle motor serves primarily to propel the vehicle, where the motor should operate to save energy to the extent possible, such a modification of the motor speed based on the parameters of the vehicle air pressure system is undesirable.

The invention is based on the objective to propose a process to adjust the maximum rotation speed of a working machine, which improves on the state of the arts, which is particularly reliable and which reduces the requirements for apparatus relative to known solutions. In addition, a hydrodynamic coupling is to be proposed, which is suitable for use in such a process. Specifically, the process of the invention is intended to limit the maximum rotation speed of an air compressor in a vehicle, where the air compressor is embodied specifically as a reciprocating piston air compressor and is advantageously powered by the vehicle motor, specifically an internal combustion engine.

The objective of the invention is solved by a process according to Claim 1 and by a hydrodynamic coupling according to Claim 5. The subsidiary claims describe advantageous and particularly useful embodiments of the invention.

The invention is used specifically for an air compressor powered by the internal combustion engine of a motor vehicle, where the compressor supplies the vehicle compressed air system. Due to the wide range of rotation speeds of the motor and the requirement that the air compressor is powered at sufficiently high rotation speeds even at low motor speeds, normally the gear ratio of a transmission, which is situated in the drive train between the motor and the impeller of the hydrodynamic

coupling, is chosen high enough such that the working machine, i.e. the air compressor, is operated at a sufficiently high rotation speed, even if the motor and thus the output shaft of the transmission that drives the impeller operate at low rotation speeds. It needs to be noted here that there will be considerable slip between the impeller and the turbine wheel of the hydrodynamic coupling at a low rotation speed of the impeller of the hydrodynamic coupling, which means that the impeller will rotate at considerably higher speed that the turbine wheel. For example, the impeller rotates at last twice as fast as the turbine wheel. If now the current operating characteristics of the vehicle lead to a higher rotation speed of the motor, possibly doubling or tripling, the rotation speed of the impeller of the hydrodynamic coupling will increase in proportion. This increase in speed of the impeller will significantly reduce the slip of the hydrodynamic coupling. At the same time, essentially or exactly the same load applies to the turbine wheel, given that the load requirements of the air compressor are completely or essentially identical. As a result, this application is subject to the danger that the working machine may be operated at excessive speeds.

The process of the invention or the coupling of the invention acts at this juncture as a regulator such that excessive speeds of the working machine, specifically the air compressor, which may be embodied as a reciprocating piston air compressor, will be prevented with certainty. The process of the invention determines a suitable rotation speed in the shaft between the motor and the working machine. For example, this may be the rotation speed of the working machine, the output side of the hydrodynamic coupling, the input side of the hydrodynamic coupling and/or the rotation speed of the motor. The rotation speed of the motor is defined here as the rotation speed of a suitable shaft of the motor or of a transmission powered by this motor, specifically the output side of the transmission, which drives the impeller of the hydrodynamic coupling directly or indirectly. Depending on the maximum rotation speed of the working machine, given its design characteristics, a maximum value is established and is set as the upper limit for the operating speed range of the working machine. The current rotation speed of the working machine will be monitored continuously or in intervals and will be compared to the established maximum value. Once the monitored rotation speed exceeds the established maximum value, the amount of working medium in the working space of the hydrodynamic coupling is reduced automatically by actively opening an outlet connected to the working space or by suitably modifying the flow to the same.

It is advantageous that the hydrodynamic coupling is embodied as a clutch, which means that it can be filled and emptied with working material in a controlled manner. Filling is defined here as a complete or at least a partial filling. Emptying includes in this invention a complete emptying or an emptying down to a specified remainder of working medium in the working space. This makes it feasible to transfer torque from the impeller to the turbine wheel in a first situation, namely when the working space is partially or completely filled, and to transfer no or essentially no torque from the impeller to the turbine wheel in a second situation, namely when the working space is completely empty or is emptied except for a specified remainder of medium. In a special configuration, a predetermined (small) amount of working medium is fed through the hydrodynamic coupling, even if the working machine is not powered, in order to cool the hydrodynamic coupling. However, the hydrodynamic coupling will normally be emptied completely, because such cooling is often not needed.

In a first embodiment of the process of the invention, the amount of working medium in the working area of the hydrodynamic coupling is automatically reduced in reaction to a signal of excessive rotation speed by automatically opening a centrifugally controlled valve, which is at least connected to the working space such that it conducts fluids or which opens into the working space. For example, this centrifugally controlled valve may rotate with the rotation speed of the impeller, and the centrifugal forces automatically open the valve after a pre-specified maximum rotation speed has been reached, such that working medium exits from the working space. Because the rotation speed of the turbine wheel thus will always be less than the trigger rotation speed of the centrifugally controlled valve in the impeller, a sure rotation speed check of the working machine, which is in a mechanical connection with the turbine wheel, can be achieved.

A hydrodynamic coupling according to the invention, which may be used in the process of the invention, will thus have a centrifugally controlled valve that is included most advantageously in the impeller, that opens above a certain rotation speed and that permits the removal of working medium from the working space.

A second embodiment of the process of the invention may control the rotation speed without the assistance of a valve. This embodiment of the invention is based on the insight that the meridian flow in the working space of the hydrodynamic coupling is modified by the rotation speed of the hydrodynamic coupling, specifically the impeller of the hydrodynamic coupling. Thus, at least one port of at least one outlet is situated in the working space of the hydrodynamic coupling on the inner circumferential surface such that the meridian flow largely or fully moves past this port at low rotation speed of the impeller, specifically in the direction of the radial circumference, such that no or at worst very little working medium enters into the port and thus exits from the working space. However, at high rotation speeds, the meridian flow in the working space adjusts such that the port is in line with the tangential direction of the meridian flow, such that working medium is pressed into the port by the meridian flow and thus exits from the working space via the outlet. Specifically, given that low slip implies that the meridian flow is further to the outside of the paddle profile of impeller and turbine wheel, which means that the tangential direction on the radial inner circumference of the meridian flow in the working space moves radially to the outside, the working medium will flow directly into the port of this outlet, given the positioning described by the invention for this one or more outlets, which is precluded at lower rotation speeds by the fact that there is no or essentially no dynamic pressure of working medium into the port.

A hydrodynamic coupling of the invention, which is suitable for use in the second embodiment of the process of the invention, has the port of an outlet on the inner circumference of its working space, where the port is situated in the second rising quadrant of the impeller. This location specification derives from a theoretical subdivision of the circumference of the working space in an axial cross section through the hydrodynamic coupling into four quadrants, starting with the first quadrant on the radial interior of the impeller; then the second quadrant follows in the direction of the established meridian flow at the propulsion of the impeller on the radial exterior of the impeller. The working medium then flows from the second quadrant into the third quadrant, which extends to the radial exterior of the turbine wheel and is subsequently slowed radially to the interior into the fourth quadrant, which extends to the radial interior of the turbine wheel.

In order to assure that the working medium passes over the port at low rotation speeds of the impeller, such that no or essentially no working medium enters into the port to be removed from the working space, it is feasible to add a protuberance that extends to the interior just prior to the port, viewed in the direction of flow, where this protuberance is designed on the inner surface of the

impeller. A flow of the working medium through the port can be prevented, particularly if this protuberance has the shape of a ramp, as will be described in more detail by reference to the following figures.

Advantageous positions of at least one port in the second quadrant of the impeller are positions between 120 and 150 degrees, specifically between 130 and 140 degrees, preferably at exactly or roughly 135 degrees. The degree specifications refer to the radian measure, viewed from the radial interior in the impeller, beginning in a manner of speaking at the foot of the working space in the impeller continuing in a circumferential direction radially to the exterior to the radial outer edge of the impeller, where 180 degrees are reached.

The invention will be described in more detail in the following by reference to an embodiment example.

The figures are:

FIG. 1 three schematic operating conditions of a hydrodynamic coupling of the invention, starting with a low rotation speed and progressing to a medium rotation speed to a high rotation speed;

FIG. 2 an enlarged detail from FIG. 1, where the port of the invention in the impeller can be seen;

FIG. 3 the rotation speed of an air compressor (compressor) relative to the rotation speed of the motor of the vehicle;

FIG. 4 the associated diagram of the characteristic curve of the hydrodynamic coupling of the invention.

FIG. 1 depicts a schematic of hydrodynamic coupling 11, which is part of the power transfer from motor 10 to working machine 12. Motor 10 includes here an internal combustion engine 10.1 with an associated transmission 10.2. An output shaft of transmission 10.2 is connected to the input side 11.1 of hydrodynamic coupling 11, consisting of impeller 1. The output side 11.2 of the hydrodynamic coupling, consisting of turbine wheel 2, is connected to working machine 12, which is an air compressor. Of course, it is possible to integrate another transmission or a step-up/down gear in the connection between motor 10 or transmission 10.2 and impeller 1 and in the connection between turbine wheel 3 and working machine 12 in order to achieve the desired ratio of rotation speed. It is also feasible to integrate a single transmission or a step-up/down gear on only one side of coupling 11.

FIG. 1 a depicts schematically the situation of hydrodynamic coupling 11, where impeller 1 is powered by motor 10 at a relatively low rotation speed. As a consequence, there will be considerable slip between impeller 1 and turbine wheel 2, for example, and a ratio of rotation speeds between motor 10 and the working machine 12 (the compressor) as is depicted on the left side of the graph shown in FIG. 3.

At such low rotation speeds of hydrodynamic coupling 11, there will be relatively large amount of slip between impeller 1 and turbine wheel 2, as is depicted, for example, on the right side of the graph in FIG. 4. The letter “n” in FIG. 4 indicates the rotation speed of the impeller, where slip decreases with increasing rotation speed, as shown by the heavy arrow in FIG. 4.

FIG. 1 b depicts schematically the situation of the same hydrodynamic coupling 11 as is shown in FIG. 1 a, but at a higher rotation speed. There is a noticeable meridian flow within working space 3, but this meridian flow still covers the entire inner surface of working space 3, viewed in an axial cross section.

FIG. 1 c depicts the same coupling 11 at a high rotation speed, specifically a higher rotation speed than is depicted in FIG. 1 b. It is easy to see that the meridian flow in working space 3 has shifted radially towards the outside compared to the situation in FIG. 1 b, which means that the inner circumference of the meridian flow in working space 3 has migrated radially towards the outside. Viewed in an axial cross section through working space 3, the resulting meridian flow 5 has a tangential flow to its inner circumference that points directly into the port of outlet 6, such that the resulting dynamic pressure presses the working medium into the port of outlet 6 and thus through outlet 6.

FIG. 2 shows an enlarged detail of working space 3 in the area of impeller 1. It is easy to see that there is a protuberance on the inner circumference of working space 3 in impeller 1 just ahead of port 6.1 of outlet 6 viewed in a radial direction, which extends radially into the interior of working space 3. This protuberance 7, which has the shape of a ramp, has the function of ensuring that no or essentially no working medium exits through outlet 6 at rotation speeds below the maximum permissible rotation speed of the impeller, but rather to ensure that meridian flow 5 flows across port 6.1 in the radial circumference direction.

As FIG. 3 shows, working space 3 can be sectioned into quadrants in the depicted axial cross section through working space 3, of which the first quadrant I and the second quadrant II divide the area of working space 3, which is located in impeller 1, into two equal parts.

The first quadrant I is here radially within the second quadrant II, where the two quadrants I, II are mirror images of each other on a mirror plane parallel to the axis.

As depicted, port 6.1 of outlet 6 is roughly or precisely in the center of the arc that forms the inner surface of the outer circumference of working space 3 in the second quadrant II. Expressed in degrees, this means that port 6.1 will be located at roughly 135 degrees, namely in the center between the radial inner start of the second quadrant II at 90 degrees and the radial outer end of quadrant II at 180 degrees.

FIG. 4 shows that the Lambda value, which is also known as the coefficient of performance of hydrodynamic couplings, decreases at increasing rotation speeds of the impeller or the turbine wheel, where the rotation speed of the turbine wheel is a function of the rotation speed of the impeller and the slip of the hydrodynamic coupling. At a slip of just below 10 percent, which means that the turbine wheel runs with a rotation speed that is one-tenth of the rotation speed of the impeller, the characteristic curve breaks down and there is no additional reduction of slip. 

1. A process to regulate the maximum rotation speed of a working machine, specifically an air compressor in a vehicle, where working machine is powered by motor via hydrodynamic coupling, which contains a working space that is filled partially or fully with working medium to transfer torque from an input side with impeller to an output side with a turbine wheel, including the following steps: monitor the rotation speed of working machine, of output side of hydrodynamic coupling, of input side of hydrodynamic coupling and/or of the motor; specify a maximum permissible value for the rotation speed and compare it to the monitored rotation speed; reduce the amount of working medium in working space of hydrodynamic coupling automatically by opening or flowing through an outlet connected to working space, if the monitored rotation speed exceeds the maximum permissible value; characterized by having the reduction of the working medium in working space result from a shift of meridian flow of working medium in working space in a radial direction towards the exterior into a position in which port of outlet in working space, which is designed to remove working medium from working space, is in line or essentially in line with the tangential direction of meridian flow, such that the working medium exits from working spaced by direct flow into port, whereas meridian flow largely or completely flows across port at rotation speeds less than the maximum permitted value.
 2. The process of claim 1, characterized by having working machine, which is embodied as an air compressor in a vehicle, provide input to a compressed air system of the vehicle and by having working machine toggle between a working status, in which it is powered via the partly or fully filled working space of hydrodynamic coupling by motor, which can also power the vehicle and which is specifically embodied as an internal combustion engine, and a rest status, in which it is disconnected from the power of motor by the action of working space of hydrodynamic coupling that is completely empty or empty except for a specified remainder of working medium.
 3. A hydrodynamic coupling for use in a process as described in claim 1, where the coupling has the following characteristics: an impeller and a turbine wheel, which together form a toroidal working space; working space can be filled with a working medium to transfer torque from impeller to turbine wheel; the interior surface of working space contains a port of an outlet; port is located in the second rising quadrant of impeller, viewed in an axial cross section of working space and in the direction of meridian flow in working space.
 4. The hydrodynamic coupling of claim 3, characterized by having a protuberance on the interior surface of working space in front of port, specifically directly adjacent to port, viewed in the direction of meridian flow.
 5. The hydrodynamic coupling of claim 4, characterized by having a ramp-like shape on protuberance, viewed in the direction of meridian flow.
 6. The hydrodynamic coupling of claim 3, characterized by having port on the radial circumference surface located between 120 and 150 degrees and specifically between 130 and 140 degrees, starting radially in the interior of working room in impeller.
 7. A hydrodynamic coupling for use in a process as described in one of claim 2, where the coupling has the following characteristics: an impeller and a turbine wheel, which together form a toroidal working space; working space can be filled with a working medium to transfer torque from impeller to turbine wheel; the interior surface of working space contains a port of an outlet; port is located in the second rising quadrant of impeller, viewed in an axial cross section of working space and in the direction of meridian flow in working space.
 8. The hydrodynamic coupling of claim 4, characterized by having port on the radial circumference surface located between 120 and 150 degrees and specifically between 130 and 140 degrees, starting radially in the interior of working room in impeller.
 9. The hydrodynamic coupling of claim 5, characterized by having port on the radial circumference surface located between 120 and 150 degrees and specifically between 130 and 140 degrees, starting radially in the interior of working room in impeller. 